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Voodoo....
I took a quick and dirty sample of 978 UAT data tonight using the IFLY data rate dialog. One tower only from the comfort of my back porch. The data seems to support what I saw in the plane today - that a longer antenna with length of ~7.75-8.25 inches from transition of plastic base to metal antenna provides a better data transfer rate.
Methodology - Antenna length was set and then data taken at 10 sec intervals for 4 intervals. I'll try it again later - not intuitive at all...happy to be proven wrong ![]() ![]() |
Stratux user report w Foreflight, 11 hrs X-country
Quick Labor Day weekend x-country, Houston to Ft. Benning and back. 11 hours flight time including VFR weather deviations.
At altitudes above 500', every time I checked FFlight indicated at least 1 tower, most frequently 3 or more. Also used flight following on every leg. Cruise altitudes were 1000', 2.5K, 3.5K, 4.5K, and 5.5K. I taped the Stratux antenna to the top of the passenger seat seatback, behind her left shoulder, with antenna un-extended, and battery/R Pi sat on the baggage compartment floor. In eleven hours I only saw traffic in my vicinity twice, in the Houston area, and a single plane I was overtaking while enroute at 3.5K near Montgomery AL. Maybe cumulative view of traffic for 20 minutes time in 11 hours of towers in view. Did see distant weather at least a few of the hours. I still see value in keeping/buying XM Wx on my 496, and look forward to more ADSB-out aircraft "pinging" the ground stations so traffic appears more consistently. Pleased to have another tool to increase Situational Awareness, and it does indeed provide traffic and weather information to Foreflight on a 64 gB iPad2 for a one-time cost of around $120. My GPS position comes from the BadElf chip plugged into the iPad2 charging/data connector. Since the Pad 2 battery has weakened I supplement power with USB "recharger" packs. It would really be nice if FFlight would audio announce that ADSB identified traffic is within a certain range of your position. That annunciation could draw your attention to the display. Carl |
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Must reports I have seen have it the antenna at 5.5 to 5.75 inches |
Anyone have it working on FlyQ V2.0 ? I know you have to change the SSID to "Stratus12345" for it to recognize it but the app loses traffic after about 30 seconds.
Rock solid on WingX the complete time. |
Pete it looks like you've rediscovered the 5/8 wave antenna. You should be able to increase your efficiency some with an impedance matching network. I'm curious to see how it performs in the air. The sensitivity directly above and below you will probably suffer (I'm guessing TIS-B traffic is broadcast from the nearest ground station). You could get some data on the ground by tilting the antenna towards or away from the ground station to look at the gain at various elevation angles.
Paige |
Hi Paige,
I'm not an RF guy. I always look for experts when this stuff comes up. I tried to do some reading and came up dry. Everything I read about impedance matching focuses on transmit efficiency. Can you point me to a book or document or internet page that goes into the specific influence of impedance matching on a receive-only system? Thanks. |
Future Growth?
There's now a 7" touch screen available.
That is, it's available for the Raspberry Pi, not the Stratux. So far. Dave |
Data looks reasonable.
Pete,
Your data makes sense for 1/2, 5/8, & 3/4 wavelength antenna lengths. These are the lengths I calculate for 978MHz: Speed of light 299792458 Frequency 978000000 Antenna length in inches. Full wave: 12.06820977 3/4 wave: 9.051157327 5/8 wave: 7.542631106 1/2 wave: 6.034104885 1/4 wave: 3.017052442 Looks like 1/2 wave and above really helps. Not an antenna expert just following a basic calculation. Dave |
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Noise also enters into the equation in receive systems, so sometimes the best signal to noise ratio is achieved when the receiver's internal matching network is adjusted for best noise performance instead of maximum power transfer, but that's the radio designer's problem. You can basically treat the receiver as a black box that expects to see an antenna of a specific impedance (usually 50, sometimes 75 ohms). The best you can do is match the antenna to the transmission line (coax) to the receiver. If you don't, you lose power and increase noise. Here's a pretty extreme example from google books:https://books.google.com/books?id=6-...figure&f=false |
I finally got back to booting up the latest image installed from pi_filler macbook pro.
On bootup, I select option 1, for using the remainder of the sd card as writeable. Then, I was prompted for the userid & password. I remember the uid = pi, and pwd=null. no go on the null password. Can someone chime in? |
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